That's why we play with the 1 is an auto fail rule.
But that's saying there's always a minimum 5% chance of failure at doing anything. That's a ridiculously high rate of failure for someone who's supposed to have devoted his life to improving that skill and that's what that someone did, spending so much resource on his skill that rolling a 1 is still going to pass the DC.
Even for difficult, complicated tasks, 5% failure rate is unacceptably high. I'm sure you'd agree that piloting and landing a commercial jet is a difficult task, but we don't have 5% of planes crashing everyday.
Actually I'm describing reasons why someone may fail at something they are normally good at.
But those cases are usually so uncommon that it's less than 5%. The d20 simply isn't granular enough to cover those rare cases of failure.
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